post-replication repair RAD18 and RAD6 genes are involved in the prevention of spontaneous mutations caused by 7,8-dihydro-8-oxoguanine in Saccharomyces cerevisiae

• Published in: Nucleic acids research 2004-01, Vol.32 (17), p.5003-5010
• Main Authors: Padula, M. de, Slezak, G, Kemp, P.A. van der, Boiteux, S
• Format: Article
• Language: English
• Subjects: Base Pair Mismatch; DNA Glycosylases - genetics; DNA Repair; DNA Replication; DNA-Binding Proteins - genetics; DNA-Binding Proteins - physiology; DNA-directed DNA polymerase; DNA-Directed DNA Polymerase - physiology; genes; Genes, Fungal; Guanine - analogs & derivatives; Guanine - metabolism; mutagenesis; Mutation; RAD18 gene; RAD6 gene; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - physiology; Ubiquitin-Conjugating Enzymes - genetics; Ubiquitin-Conjugating Enzymes - physiology; yeasts
• ISSN: 0305-1048; 1362-4962; 1362-4962
• DOI: 10.1093/nar/gkh831

7,8-Dihydro-8-oxoguanine (8-oxoG) is an abundant and mutagenic lesion produced in DNA exposed to free radicals and reactive oxygen species. In Saccharomyces cerevisiae, the OGG1 gene encodes the 8-oxoG DNA N-glycosylase/AP lyase (Ogg1), which is the functional homologue of the bacterial Fpg. Ogg1-deficient strains are spontaneous mutators that accumulate GC to TA transversions due to unrepaired 8-oxoG in DNA. In yeast, DNA mismatch repair (MMR) and translesion synthesis (TLS) by DNA polymerase η also play a role in the prevention of the mutagenic effect of 8-oxoG. In the present study, we show the RAD18 and RAD6 genes that are required to initiate post-replication repair (PRR) are also involved in the prevention of mutations by 8-oxoG. Consistently, a synergistic increase in spontaneous CanR and Lys+ mutation rates is observed in the absence of Rad6 or Rad18 proteins in ogg1 mutant strains. Spectra of CanR mutations in ogg1 rad18 and ogg1 rad6 double mutants show a strong bias in the favor of GC to TA transversions, which are 137- and 189-fold higher than in the wild-type, respectively. The results also show that Polη (RAD30 gene product) plays a critical role on the prevention of mutations at 8-oxoG, whereas Polζ (REV3 gene product) does not. Our current model suggests that the Rad6–Rad18 complex targets Polη at DNA gaps that result from the MMR-mediated excision of adenine mispaired with 8-oxoG, allowing error-free dCMP incorporation opposite to this lesion.